Most organisms respond to stimulus in their environment by movement (taxis) toward or away from the stimulus; yet the molecular mechanism of taxis is poorly understood in any organism. The simpler the behavior, the greater is the hope of defining the biochemical events of the sensory-motor network. Therefore, I propose to explore bacterial behavior, chemotaxis (movement toward or away from chemicals) in Bacillus subtilis and chemotaxis and phototaxis (movement toward light) in Rhodospirillum rubrum. The ultimate objective is to describe the behavior in molecular terms. In particular, I ask such questions as the following: What is the mechanism by which information is transmitted from receptors to flagella? How do receptors--photoreceptors or chemoreceptors--generate this signal? The immediate experiment's objectives of work include the following: (B. subtilis) 1) correlate degree of methylation of certain membrane proteins (using SDS acrylamide gel electrophoresis) with enhanced swimming due to adding attractant or enhanced tumbling due to adding repellent; 2) isolate and characterize the alanine chemoreceptor; 3) isolate and characterize mutants in chemotaxis to amino acids and sugars; (R. rubrum) 4) develop assay of phototaxis and, with mutants in each process, define relation between phototaxis and photosynthesis; 5) evaluate role of membrane potential, divalent cation, and methylation of membrane proteins in control of frequency of reversals.